Re: [PATCH] Stop ALTER SYSTEM from making bad assumptions

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, David Fetter <david(at)fetter(dot)org>, Ian Barwick <ian(dot)barwick(at)2ndquadrant(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [PATCH] Stop ALTER SYSTEM from making bad assumptions
Date: 2019-08-05 16:53:37
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On 2019-08-05 12:43:24 -0400, Tom Lane wrote:
> Yeah, good point. There are a lot of other cases where you really
> don't want system startup to happen, too.


> On the other hand, people have also opined that they want full error
> checking on the inserted values, and that seems out of reach with less
> than a full running system (mumble extensions mumble).

I think the error checking ought to be about as complete as the one we
do during a normal postmaster startup. Afaict that requires loading
shared_preload_library extensions, but does *not* require booting up far
enough to run GUC checks in a context with database access.

The one possible "extension" to that that I can see is that arguably we
might want to error out if DefineCustom*Variable() doesn't think the
value is valid for a shared_preload_library, rather than just WARNING
(i.e. refuse to start). We can't really do that for other libraries, but
for shared_preload_libraries it might make sense. Although I suspect
the better approach would be to just generally convert that to an error,
rather than having some startup specific logic.


Andres Freund

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